Football unit is a term used to describe the group of players that make up a football team. A YARD is a unit of measurement equal to three feet, and is commonly used in American football to measure the distance a team must travel to gain a first DOWN. DOWN is a term used to describe the number of chances a team has to advance the ball in American football. HALF is a term used to describe the two equal parts of a game in American football. ELEVEN is the number of players on the field for each team in American football.